A turboprop of the above-mentioned type needs to include a system for adjusting the pitch of the blades so as to be capable at all times of adapting the power of the engine to its conditions of use. In the past, systems for controlling blade pitch have been proposed in which control elements are arranged on the axis of the engine, i.e. more particularly in the central space of the annular turbine driving the blades. In most conventional manner, the turbine is of the type having two contrarotating free rotors and each rotor is connected to a rotary support on which the blades of the two propellers are installed.
The two rotary supports are thus contrarotating supports that are axially offset along a common axis, and when the blade pitch control means are situated in the vicinity of the turbine axis, it is necessary to provide an intermediate mechanical device for controlling the pitch of the blades through the rotors of the turbine. That mechanism is heavy, expensive, and difficult to maintain.